The present invention relates to apparatus for coupling electrical energy into and/or out of a surface acoustic wave ("SAW") device. More particularly, the present invention relates to apparatus for coupling energy into and out of a SAW device which serves as a transponder in a "passive interrogator label system".
A "passive interrogator label system", so called, is a radar system utilizing transponders which are capable of receiving an interrogating first signal, processing this signal and transmitting a second signal in reply that is derived from the first signal and contains encoded information. Because the encoded information normally includes an identification code which is unique to each transponder, and because the transponders of such a system are relatively light weight and small and may be easily attached to other objects to be identified, the transponders are sometimes referred to as "labels". Furthermore, the transponders, which may be implemented by SAW devices, carry no self-contained power source, such as a battery, that must be periodically replaced. Consequently, these transponders are "passive"; hence the name "passive interrogator label system".
Passive interrogator label systems of the type to which the present invention relates are disclosed in the following U.S. patents:
______________________________________ U.S. Pat. No. Patentee ______________________________________ 3,273,146 Horwitz, Jr. 3,706,094 Cole et al. 3,755,803 Cole et al. 3,981,011 Bell 4,058,217 Vaughan et al. 4,059,831 Epstein 4,263,595 Vogel ______________________________________
Such systems are also disclosed in the commonly-owned patent applications referred to above. In general, a passive interrogator label system includes an "interrogator" for transmitting a first radio frequency signal; at least one passive transponder which receives this first signal, processes it and sends back a second radio frequency signal containing encoded information; and a receiver, normally located next to the interrogator, for receiving the second signal and decoding the transponder-encoded information.
The aforementioned U.S. patent application Ser. No. 793,703 discloses a "package assembly" comprising a SAW device and a dipole antenna electrically connected to two terminals formed by contact pads on the SAW device. The dipole antenna is formed by a metal foil, cut to the proper size and shape and bonded by heat and pressure to a polyethylene coated Mylar sheet. Each individual "pole" or element of the dipole antenna is serpentine shaped.
The antenna characteristics required for this application determine that each pole be approximately 1 inch wide and 1 1/2inches long. With the SAW device placed at the center between the two poles extending in opposite directions, the entire assembly or "label" formed of the SAW device and the antenna is approximately 1 inch wide and 3 inches long.
Whereas this flat, card-like structure is ideal for many applications such as identification badges for personnel, and I.D. tags for automobiles, factory parts or the like, certain applications require that the antenna be shaped or configured differently so as to meet certain performance requirements or to permit the assembly to fit within available space. Consequently, it is necessary to couple the SAW device to a large variety of antenna configurations in a mass production mode. Not only are the requirements for mass production severely impaired by the necessity of connecting the SAW device to one type of antenna or another, but the sensitive, fragile nature of the SAW device itself makes chip handling difficult.